disk: convert part_* files to COBJ-$(CONFIG_XXX) style

Move the CONFIG_XXX out of the part_XXX.c file and into Makefile to
avoid pointless compiles.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/disk/part_mac.c b/disk/part_mac.c
index 1922fe5..c1afc8c 100644
--- a/disk/part_mac.c
+++ b/disk/part_mac.c
@@ -34,12 +34,12 @@
 #include <ide.h>
 #include "part_mac.h"
 
-#if (defined(CONFIG_CMD_IDE) || \
-     defined(CONFIG_CMD_SCSI) || \
-     defined(CONFIG_CMD_SATA) || \
-     defined(CONFIG_CMD_USB) || \
-     defined(CONFIG_MMC) || \
-     defined(CONFIG_SYSTEMACE) ) && defined(CONFIG_MAC_PARTITION)
+#if defined(CONFIG_CMD_IDE) || \
+    defined(CONFIG_CMD_SCSI) || \
+    defined(CONFIG_CMD_SATA) || \
+    defined(CONFIG_CMD_USB) || \
+    defined(CONFIG_MMC) || \
+    defined(CONFIG_SYSTEMACE)
 
 /* stdlib.h causes some compatibility problems; should fixe these! -- wd */
 #ifndef __ldiv_t_defined